US1497543A - Adsorptive carbon and process of making the same - Google Patents

Description

Planefun@ 10,' y1924;

Newcomers KLCHANEY, oF LAxEwoop, or'I'Io.

' AnsoRPTIvE Vcannon annrnocass'or M sxrNerHni sama Continuation of application Serial No. 251,263, filed August 24, 1918.. This application led .Tune ,30, 19-19,

'Serial N'o.v 307,620.

To all whom it mag/concern'.

Be it lnown that I, vNnwcoM K. CI-IANEY,v

acitizen of the United States, residing at Lakewood, -in thecounty of Cuyahoga and .State'of'r'Oh'id have invented certain new.

and useful Improvements in Adsorptive Carbon and Processesof Making the Same,

f of which the following is a specification.

This invention relates to processes of manufacturing highly active adsorbent carbon,l

and to the novel from. A

It has long been known that manykinds of charcoal will absorb gases, and that cerlain charcoals have a much greater capacity than others for taking up gases. The sorbed gas is readily expelled from most varieties of charcoal, for exampleA by blowing 'air products resulting there- 1 through it; So far as I am aware, the greater capacity of certain carbonaceous residues for sorbmg gases has always been .ascribed to the particular organic materials from i f which they were derived; andV it.\vas considered that high capacity was not possessed by and could not be imparted to otherforms fof carbon, such for example as carbon "derived from hard orsoft coals or other relatively cheap and abundant materials. While Vthis was universally accepted as a'fact, the

reasons therefor were not known.

I have now discovered that the foregoing assumption is erroneous, and that by the proper application of certain basic 'principles herein disclosed it is possible to obtain, a highly adsorptive carbon from a very wide variety of natural carbonaceous or carbon-.containing materials including such deposits of mineral carbon as are not essentially graphitic in character. In fact, operating in accordance with these principles, vI am able toprepare from ordinary hard 0r softA coal an active carbon which is far more adsorptive ot gases than the bestbone or wood charcoal heretofore available. Simi lar1y, I am enabled to prepare from vegetable'or animal products a form-.of carbon o f greatly enhanced activity as regards adsorptive capacity for gases. These novel forms of carbon are' susceptible of many industrial .and military uses, including their use in defensive warfare against chl'oipicriu, phosgene and other toxic gases' which from a practicalfpoint of view are not adsorbed fatali byjthe varieties Iofcharcoal heretof.

fore'l available,

Carbon may exist either in anwactiveor in annactive modification as regardsffad? sorptive capacity for gases.- Inactive carbJon 1s relatively reslstant to oxidation, and

possesses to some degree certain of' the charample in the so-called gas-treating of coke. The temperature above which carbon 1s deposited 1 n the-lnactlve vmodification by the thermal decomposition of hydrocarbons cannot be stated in absolute terms, since 1t Varies-rather widely according to the furnaeing conditions, but in general it may be said that carbon is deposited iu the active modification iat temperatures below about W-600o C., whereas at temperatures materially exceeding ,6009 C. a

',TENT omer.

strong 'tendency exists toward the deposition-of the inactive modiIicat-ion. Inactive carbon cannot, so far as now knowinbe eifectively activated by anycommcreially pra- 54 lieable method.

Active carbon is formed therefore whencvercarbon is deposited at relatively low temperatures by chemical or thermal decomposition of carbon-bearingmaterials. However, active carbon possesses an extremely high adsorptive capacity for hydrocarbons and as usually repared it is practically saturated with ad) prevent it from adsorbing other gases. It

-i`ollows therefore'thatmany carbona'eeous productsfwhich actually contain a high pros orbed hydrocarbons, which portion of active carbon are apparently in acli've, or at most exhibit a low degree ofactivitv. I have found however .that if these adsorbed hydrocarbons arejsubstautially removed, without, in the process of their. removal,I giving'rise to deposits of inactive carbon, the resulting hydrocarbon-free material possesses extremely high activity or adsorpt-ive capacity. As stated before this activity isquite independent of the origin of the carbon, provided it be not originally graphitic. d

For clearness, -I designate an active carlbon base containin' adsorbed hydrocarbons .as a primary fear on.-. -Many vcommercial grades of animal audyegetable charcoal lare of this character; se also are such cokes as result from the low-temperature distillation of |bituminous coals', mineralrbitumens or the like. Ordinary coke on the other hand is heavily charged With inactive'carbon reregarded, althoughthe hydrocarbons are usuall present in such coals in great excess of t e adsorptive capacity. of the active carbon base, and such excess may be readily removed by distillation under proper conditions. A primary carbon is therefore essentially anV adsorption-complex consisting of hydrocarbons adsorbed by a base of active carbon, with or Without associated nonadsorbed hydrocarbons.. 4

My process may be regarded a starting with a primary carbon as defined above, yWhether of animal, vegetable or mineral origin, and Whether native or artificiallyv preared, yitbeing essential only that it should e, for practical purposes, free from inactive carbon deposits such ras 'result from gas treating. My invention contemplates such`- further treatment yof primary carbons asl will eliminate adsorbed hydrocarbons, While leaving the active carbon base free from deposits of inactive. carbon. In its preferred embodiment my invention further contemplates such treatment of the residual active carbonbase .as will increase the surface of the particle per unit ofvolume,this increase ,of surface relative to volume being preferably carried tothe maximum attainable de- ,gree for carbom particles of a given size or grading.

v I will now describe e'rence to` a specific embodiment thereof, starting with a suitable primary carbon which should preferably havea relatively high ap arent density, for example an apunderlying this choice of a dense primary carbon is ,explainedbelow Such material `my invention by ref-l may beprepared forv example by the dis# tillation of bituminous coal or the denser cellulosic materials, bone 'or the like at temperatures not materially exceeding 500- 600 C., with proper precautions to eliminate all of the bituminous matter or hydrocarbons which can be volatilized at this temperature. If desired oxidizing conditions may be maintained during the distillation, order to minimize the proportion of adsorbed hydrocarbons in the residual active carbon base. The-heat should `be applied as uniformly and regularly as possible, particularly avoiding any materixil amount of gas-treatment due to the hydrocarbons \'being cracked at local areas of higher temperature with deposition of Iinactive carbon. 01' as stated above anthracite coalmay be used directly as a primary carbon.

While bone is mentioned above to illustrate the general applicabilityv of the process to be described, it should be noted that char having an, exceedingly ligh ash. content, such as that produced from bones,l has en'- tirely different properties from carbons of materially lower ash content, such as an-l within mydefinition o`f primary carbon. A

simple distillation will produce fromfbones` a char in which the ash-free matter appears to have a considerable de ee of activity. This is largely due to the fact that the very liigh pro ortion of'inorganic matter present extends t e carbonaceous portion to such l degree that the exposed surface approaches a magnitude which, in the case of materials I in which carbonpredominates, can only be obtained by limited oxidation. Bone-char is therefore'not essentially a e'om lex offactive carbon and hydrocarbons, as eined above, since the inorganic matter present performs a function of very great importance', and is therefore essential. l y y Bone-char cannot be made into a material exhibiting as a whole a higli activity because the inorganic matter of which it is chiefly composed has no adsorbent action and nonecan be imparted' to it. My invention is concerned with. materials which containa predominating proportion bf matter amenable to activation, and which do not have ap composition and nstructure adapted -to render them self-activating. parent ensitykin excess of 1.0. The reason Whatever the origin of the primary carbon, I"irst subject it to a process of differerably lying between 8001000 C.,the primary carbon being preferably disposed in relatively thin layers. I continue the above described treatment until vthe exposed hydrocarbons are substantially eliminated, and I may then cool the product to such temperature that it may be discharged from the furnace without danger of burning. If the hydrocarbons.

operation has been properly carried out the product, aside from a greater or less ash .content depending upon its origin, will consist substantially of active carbon, and will be found' far more active, as regards adsorptive capacity for gases, than any charcoal heretofore available, whether of animal or vegetable, origin. The activity of-the carbon may be tested as hereinafter described'.

Gaseous chlorin iscapable of combining with and bringing about the elimination of adsorbed hydrocarbons, and may be either used `alone, or preferably in alternation with steam. .It acts therefore in this reaction essentially as an oxidizing agent, and is in'- eluded in the term as employed herein. Air

may be used, but atdecidedly lower temeratures, (around 350-450 C.) and with ess satisfactory results, especially as regards the percentage yield of active carbon.

In this connection it may be explained that in the ordinary process of distillation of rcarbonaceous materials at relatively low temperatures, active carbon is first formed by the thermal decomposition of unstable This active carbon adsorbs a further quantity of hydrocarbons, and these adsorbed hydrocarbons are thereby stabilized to a remarkable extent; so'that adequate for the they are retained under conditions of temperature, pressure, etc., at which they would otherwise be quickly eliminated. For example anthracene cannot ordinarily exist in solid or liquid phase at normal pressure at temperatures in excess of its boiling point,

360 C.; nevertheless I have found considerable quantities of a hydrocarbon essentially similar to anthracene in cedar-wood charcoal which had been reviously calcinedto 800 C. This ,aptly il ustrates the power of active carbon to stabilize its adsorbedmaterials. This also explains why ordinary distillation processes whether carried out at atmospheric or lowerpressures or even under the highest attainable vacuum, are wholly inroducftion of an active car# bon as distinguisllfed fromla primary carbon.

Y Suiiciently prolonged heating ofthe primary carbon at extreme y high temperatures will, itis true, serve partially to remove 'or break down the adsorbed hydrbcarbons, but on account of the 'stability'of the adsorption-com.- plexA the temperatures I iecessa' 'for this pur-` pose are so high that another iiicult v is encountered, namely, th'at ofso-calle u gas' treating?, which as Aabove stated results in the deposition of inactive carbon in and on the active carbon base; and since this inactive' carbon is decidedll more difficult to oxidize than is active car on, it cannot be successfully removed from the active carbon by differential oxidation. Hence it is essential to the proper practice of this process that the deposition of 'inactive carbon should be substantially avoided at every stage ofthe operation, including the production of the primary carbon. At the same time considerable latitude is v ermissible in the actual carrying out of t e4 process, for the reason that the tendency to gas-treatment has been found to vary with the chemical nature of the adsorbed hydrocarbons, that is, whether their decomposition takes place at a low or at a high temperature, the temperature at which molecular carbon is set free being apparently a controlling factor in determining 'its activity. For example methane (CIL)` cracks or gas-treats appreciably only above 700 C., and therefore yields only inactive carbon. Carbon deposited from carbon monoxid (CO) at 300 C. by the aid of catal sts is on-the other hand of the active modi cation. Acetylene (C2H2) also cracks at low temperatures, namely, around 300 C., and the deposited carbon is more or less active and can be further activated by \niy process. The hydrocarbons present in bituminous coals, are found to depositl inactive carbon much more readily than the hydrocarbons derived from certain other carbon complexes, such as may bejprepared from certain woods and nuts. Hence it is that the adsor tive carbon of commerce was heretofore'pro uced only fromithelatter sources, and not byrea- .son of'any inherent impossibility of prepar,

inlgl active carbon from coals, petroleum and ot er mineral deposits.

" The differentialoxidation of the adsorbed hydrocarbons as described above, when prop,

erly carried out, yields a carbon product hav'- ing the maximum activity per unitof surface. i However, the amount'of surface ex- -posed per unit volume of the material may vary widely, and I refer to vsubjectthe ace tive carbon, -eitherbefore or after cooling, to a further treatment by limited oxidation whereby the surface exposed per unit of volumeis brought practically to a. maximum. This I accom lish by subjecting the active carbon, after ing freed from exposed hydrocarbons, to a current of steam or other gaseous oxidizing agent, preferably at a temperature'of about 800-1000 C., the operation being continued until the apparent dntween 0.5 and 1.0; and-preferably unti the i'io apparent vdensity more or'less closelyapproxlimates the value 0.66.' I have demonstrated experimentally that this is the point at whichJ the 'article ossesses the maximum. `exposed sur i;,cerelative toitsvolume.I

The values given above are for what I term block density, that is to say the apl parent density of a carbon block or granule per se. Adsorbent carbon is generallyused in granular form and the block density difffers from the apparent density of the entire granular mass", since the latter value takes into account the voids between the granules.

,For gas warfare adsorbent carbonV is usually 'ground to pass through aNo. 8 mesh onto a No. l0 mesh Tyler standard screen. lWith this ineness the apparent density 0.66in

the 4particlescorresponds to about 0.41 apparent density of the entire granular mass.

. Since y"an apparent density of substantially 0.66 is the optimum value for adsorbent carbon,l it follows that carbon having an original density below this-value cannot be given by activation 4the maximum sorbent life under the same -test conditionsI maybe raised to 225 Nminutes, which surpasses the life of any carbon known rior to my invention. The cedar charcoal, ow-

4 ever, cannot be raised to the maxi-mum life stood that my invention is not limited to' `reducing `the apparent density of the dense of which active carbon is capable (substantially 1000 minutes) because the eect of further channelling of' the particles by oxidizing the carbon particle itself servesl only further to reduce the density, and consequently further to diminish the adsorptive capacity.

On the other hand cocoanut charcoal prepared by the usual processes has an average density of about 1.17 and the adsorbent life under the conditions previously referred to is about five ini'nutes. cocoanut charcoal inraccordance withfmy process, all of the exposed hydrocarbons can be differentially oxidized without bringing the apparent density' down to the` desired value of about`0.6`6. The oxidation can thereforebe further continued to channel out the active carbon itself and thereby to increase still further the ratio of exposed `surface to volume. If this channelling out ,l y process be continued untilthe apparent density is 0.66"the adsorbent life of the productwill be found to be approximately 1000 minutes. f It should however be under- By activating this forms of charcoal to the absolute vvalue 0.66,"

inasmuch as commerciallyractic'able results -are obtained with suc dense forms at apparent-densities lyin between 0.5 and 1.0 as previously explained. 4

It Vwill of course be understood that my invention is not limited to 4the treatment of primary c arbons having a density as high as 1.17, though cocoanut charcoal havfng a block density of this order gives ex cellent results. Whe-n primary carbons having a density as low as 0.70 are diierentially oxidized, the stabilized hydrocarbons contained therein may be substantially comlpletely removed in lmany cases' without bringing the block density below 0.50. If. the `limited oxidation be continuedbelow the lower limit of 0.5 the effect is to decreasethe exposed surface per unit of 1volume and thereby to reduce the adsorptive capacity of the product.

In view of the above between the apparent density and the yadsor tive capacity, it will be seen that. dense carbonaceous materials should preferably be selected for producing charcoal or coke or the like for this purpose. Nevertheless, I have found that the maximum adsorptive ca pacity can be imparted to charcoal, coke, lamp-black or other Aforms of carbon of low apparent density by a special briquetting procedure as follows :e

The primary carbon of low apparent density is ground'to fine powder, preferabl to pass through a 200 mesh standard Ty er screen. It is then mixedwith tar,

.pitch or other binder, molded, forced `or otherwise shaped into briquettes or. other forms, and then calcined to coke the binder. This calcination should be carried out under regulated conditions in order to avoid the deposition of inactive carbon as reviously described. After calcination Vthe riquettes are ground and activated bv the differential oxidation of the'adsorbedhydrocarbons as described above'. The product thus prepared even from light forms of primary carbon will be oundto have an apparent density above the value 0.66,l and may then advantageously be subjected to limited oxidation until this value is 'sufficiently approximated. l

Ordinary lampblack for example has4 a ,lowv adsorptive value, but by forming it into briquettes as specified a dense coke can be produced, which, on vfurther activation, has given an adsorbent life with chlorpicrin of 850 minutes* Also,the briquetting method as described above may be applied toIrelatively dense forms of primary carbon,``as for example to the fines (from coal, nut-charcoal or the like) which would otherwise be rejected for the particular purpose in view.Y In the preparatlpn of briquettes as'above described relatan' vthat no universally applicable directions for calcination can be given, since the optimum conditions may vary widely accord# ing to the type of furnace used, the weight V of the charge, the'nature ofV the original carbonaceous material and other factors. The essential point is that the calcination shouldbe carried out `without substantial gas-treatment, and in such manner as to leave the minimum practicable proportion of adsorbed hydrocarbons to be removed by the differential oxidation.

While I have referred to an adsorbent life of 1000 minutes under standard test conditions as being rthe approximate maximum value for carbonit should be understood that this statement a plies only to certain definite conditions. or example carbon ground to pass through a No. 12 screen onto a' No. 14 (Tyler standard screens) gives a greater service life than this. "gIrIowever, the standard size of granule is through No.

v8 onto No. 10 mesh so this has been adopted vin the standard test which givesr the 1000 minute life. This test .consists essentially in passing a stream of air containing one part .per thousand of chlorpicrin through a layer of 8.-10 mesh carbon ten centimeters deep,

in sufiicient quantities to pass five hundred cubic centimeters of the gas mixture per minute through one square centimeter of surface of the carbon layer, untilthe efliuent gas mixture imparts a distinct coloration to a -copper flame indicating a concentration in the neighborhood of one part per hundred thousand of chlorpicrin.

In connection with the above test it should be understood that the absorption of the gas b the car on isa arently partl. ca illary iii7 characiihr, theplgas being heid vih the capillary interstices, and partly by adsorption, the gas lbelngpresumably condensed as a lilm upon the surface of thecarbon. It is found that portions of the retained-gas may be rather readily eliminated by subjecting the mass to a current of dry air or.

other gas, whereas other portions are retained for long periods or indefinitely under this treatment. It is believed that the gas heldl by capillary absorption represents the ortion which is rather quickly eliminated y the gas current, while the -portionwhich cannot be thus washed out is that 4which is adsorbed as a ilm. An absorption -test carried out under conditions as described above may be regarded therefore as a measureof the combined capillary absorption and ilm adsorption, that is to say of the total absorptive value of the carbon.

The retentivity' ot the carbon, by which is meant its capacity for retaining the adsorbed gas may be determined by anotherform of'test consisting essentially in passing a current of drylair over the carbon, which has been previously saturatedwith chlorpicrin or other gas, 'the retentivity for which standard is 35 parts per million. Under these conditions the most active carbon prepared as hereinabove described willretain in the neighborhood of^40% of its weight ofv chIOrpiCrin, ,whereas ordinary forms of carbon will retain amounts of the order of 1% or less; and even the. recent German gasmask carbon does not` retain to exceed 10-12% under the sainetest conditions.

A modified form of the retentivity test, which can be much more quickly performed and aii'ords sharper indications, consists in first saturating the active carbon with gas at room temperaturesand then'iplacing it under high vacuum at 100o C., the charcodl being weighed at about half-hour intervals. After the capillary losses are complete, usually in the first one or two hours, the subsequent losses when charted, llie in a straight line curve. This curve, extrapolated back to theV point of origin, gives a value which may be regarded as the specific retentive capacity of the sample. The values thus obtained are much more definite and sharply re-duplicated than those obtained by the first described test, andl lie within a few percent of these values, being as a rule somewhat lower. For example samples prepared as described in this specification show under this test normalvalues of about 30-35% retentivity, with an upper limit of 40% or better. The retentivity of German charcoal under the conditions of this test does not exceed 5%.`

A betterl understanding of various matters hereinbefore referred to will be had from the accompanying drawing, whichv shows graphically -the variations in the properties ofa cocoanut charcoal oxidized with steam for various periods. The drawin includes a curve illustrating each of the ollowing:

llO

hydrogen-content of the carbon; retentivit-y y(expressed as Weight-percentare of carbon-- lt will be ,understood that the ordinates of thesaturation curve represent total sorbed vapor, and therefore include both the carbontetrachloride represented by the retentivity curve and that which is heldin the capillaries of the carbon.l The block density of the carbon diminishes throughout the test, indicating a progressive increase in-porosity, and theI 'saturation value increases continuously because [of the increase in capillary volume. The retentivity reaches a limiting value,'hoivever, indicating that beyond a certain pointA there is no further increase in surface per unit Weight ot the material, since all the evidence 'supports the view that retentivity is a surface phenomenon.

Since retentivity With reference to mass of carbon-reaches a limiting value, and since mass per 1 unit volume (density) decreases continuously,` as shown by one of the curves,

it will be apparentthat retentivity-per unit volume 6i carbon will fall offbeyond a certain maximum, as has beenl graphically shown on one of the curves. This maximum is important from the industrial and military standpointsdas the space available for g the sorbent is often strictly limited.

vIn defining my invention, however, I do not desire to be restricted to the maximum retentivity of approximately 40% of chlorpicrin, since retentive values in excess of about 20% indicatean altogether novel and highly valuable Lcommercial product. Furthermore, in accordance with my invention such retentivity is imparted to a relatively dense material, the preferred range of block density in the finished product being0. 5 to 1.0 as has already kbeen stated. Even with the density at the lower limit ofthe preferred range and-.a retentivity of only 20%, it Willl be' seen that grains of the material having an aggregate volume "of one cubic centimeter are capable of retainingf100 mg. l

ofl chlorpicrin under the described test conditions; The'retentivity referred to volume of carbon grams (exclusive of voids) differentiates the product 'ofmy invention from` cubic centimeter of grain-volume.

prior carbons even niore strikin ly than does the rctentivity referredl to Weig t of carbon, since all the .prior carbons having appreciable retentivity were of very low density. )Vhile the total absorption and the retentivity have been expressed in terms of chlorpicrin, by. reason of the necessity for having a definite standard, it is to be understod that similar general relations hold -for other gases, although of course the absolute Weights absorbed or retained will vary greatly according'to the molecular weight, specific gravity, boiling point and other physical constants of the particular gas.

Neither do l desire to be restricted to the maximum adsorbent life of ap noxiuiately 1000 minutes under thc standard test conditions described herein, since an adsorptive life in excess of 225 minutes indicates a material which is both new and useful.

This application is a continuation of my copending application-L Serial No. 251,263, filed Aug. 24, 1918.

I claim l. Process of making a highly adsorptive carbon, comprising subjecting a primary carbon, consisting essentially of an adsorption-complex of active carbon and stabilized hydrocarbons, to diiierential oxidation until the exposed hydrocarbons are substantially eliminated and the residual carbon acquires a retentive value for chlorpicrin in excess (if-20% of'it's Weight. v

2. Process of making a highly adsorptive carbon, comprising subjecting a primary carbon, consisting essentially of an adsorption-complex of active carbon and stabilized hydrocarbons, to differential oxidation until the exposed hydrocarbons are substantially eliminated, and subjecting the residual active carbon to limited oxidation untilit 'has acquired substantiallypthe 'maximu retentivity per unit of volnme i 3. `Process of making a highly adsorptive carbon, comprising subjecting a primary carbon, Yconsisting' essentially 1Otan ,adsorption-complex of active carbon and 'stabilizedl hydrocarbons, to differential oxidation'by means ofa gaseous oxidizing agent until the exposed` hydrocarbons are acretentive value Jfor chlorpicrin in excess of 20% of its Weight.

4. Process of making a. highly adsorption-complex of active carbon and stabil-ized hydrocarbons, to di'erential oxiresidual active carbon to limited oxidation until it has acquired a retentivity for chl'orpicfrinI in excess of 100 milligrams-per substantially eliminated and the residual carbon acquires" adsorptive carbon, comprisingfsubjectlng .a primary carbon, consisting essentially joffan,

izo

5. Process of making a vhighly adsorptive carbon from coal, comprising subjecting ^the coal to differential oxidation until the exposed hydrocarbon components arel substantially eliminated, and subjecting the residual active carbon to limited oxidation until it has acquired a retentivity for chlor.v

.picrin in excess df 100 milligrams per cubic y centimeter of grain-volume.

6. Process of making highly ladsorptive carbon, com rising subjecting a carbonaceous material to low-temperature distillation` to expel volatile components whilel avoiding deposition of inactive carbon, producing thereby a primary carbon consisting essentially of an adsorption-complex of active carbon and stabilized hydrocarbons,

` subjecting said primary carbon to differential oxidationk until the ex osed hydrocarbons are substantially eliminated, 'and subjecting the residual active carbon to limited oxidation until it has acquired substantially the maximum retentivity per unit of volume.

7. Process of making a highly adsorptive carbon from coal, comprising subjecting the coal to low-temperature distillation to ex el volatile components while avoiding de osition of 'inactive carbon, producin there y a primary 'carbon consisting essentially of an adsorption-complex of active -carbon and stabilized hydrocarbons, subjecting said primary carbon to differential oxidation until r the exposed hydrocarbons are substantially eliminated, and subjectin the residual active carbon to limited oxi ation.` until it has.

acquired a retentivity for chlorpicrin in excess of 100 milligrams per cubic centimeter j of grain-volume.

8. Process of making a highly adsorptive carbon `from carbonaceous materials, compris'ing grinding, bonding and shaping the carbonaceous material, calcining the ksamer.

under conditions toavoid substantial formation of inactive carbon', and subjecting'V the resulting primary/ carbon to differential oxidation until the exposed hydrocarbons are substantially eliminated, and lsubjecting the residual active carbon to limited oxidation until it has acquired a' retentivity for chlorpicrin in excess ofr milligrams per cubic centimeter of gra-in volume.

9. Process of making a `highly adsorptive carbon from carbonaceous materials of low apparent density, comprising grinding,

bonding and shaping the oarbonaceous ma4 terial, calcining the same under conditions to avoid substantiahformation ofy inactive carbon, thereby producing a primary carbon of relatively high apparent density as compared with the original material, subjecting said primary carbon to differential oxidation until the exposed hydrocarbons 'are' substantially eliminated, and subjecting the residual active carbon to'limited oxidationuntil it lasacquired a retentivity for* chlorpicrin in excess of 100 milligrams per cubic centimeter of grain-volume.

10. Process of making ahighly adsorptive I, carbon, comprising subjecting a primary" carbon having A 0:70 and consisting essentially of an adsorption-complex of activevcarbon and stabilized hydrocarbons, to differential oxidation until the exposed hydrocarbons are substantially eliminated, and subjectingthe residual ac tive carbon to limited oxidation until it has acquired substantially the Imaximum retentivity per unit of Volume.

11; Process of making a highly adsorptive carbon, `comprising subjecting a primary carbon having a block density greater than 0.70 and consisting essentially of an adsorption-complex of active carbon and stabilized a block density greater than hydrocarbons, to differential oxidation by i means of a gaseous oxidizing agent until the exposed hydrocarbons are substantiall y eliminated, and subjecting the residual active carbon to limited oxidation until it has acquired a retentivity for chlorpici'inin excess of 100 milligrams percubic centimeter of grain volume.

12. As a new {article of manufacture, highly ladsoiptive carbon substantially free from exposed hydrocarbons and from inactive carbon, having a retentivity for chlorpicrin in excess of 100 milligrams' per cubic sorptive lcarbon having a retentive value for chlorp'icrin of approximately 40% of its Weight.

16. As a vnew article of manufacture, Lhighly adsorptive carbon substantially free from exposed hydrocarbons and from inac- "tive carbon, having a block density greater than 0.50, and having a retentivity for hlorpicrinl in excess of 20% by weight.

17. As a new articleof manufacture, adsorptive carbon having an adsorbent. life in excess of 225` minutes on test comprising passing a stream of air containing one part j per thousand of chlo'rpicrin through a layer of 8-10' mesh carbon ten centimeters `deep, in suliicient quantities 'to pass five hundred I,cubic centimeters of the gas mixture? per minute-through one square centimeter of surface of thev carbon layer, until the eluent gas mixture imparts'a distinct coloration to a copper flame. A y

18. As a newvarticle of manufacture, acls orptivecarbon in gravnul-u form having an 'minute through one squarev centimeter of adsorbent' lifo' for chlorpcrin approximatsurface of lthe carbon layer, until the effluent 10 ing 1000 minutes on testcomprising passing gas mixture imparts a distinct coloration to a stream of air containing one part per a copper flame. thousand of chlorpici'in lthrough a layer of 'In testimony whereof, I ax my signa@ 8-10 mesh carbon ten centimetersdep, in ture.

su'fcient quantities to pass v'e hundred cubic 'centimeters of the gas mixture per NEWCOMB K. CHANEY.

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